What table you use really depends upon the end use of the services.
Typically, if you are just servicng a small telephone group then ERLANG B would suffice. If you are providing a queue facility wherby callers are queued until answer (ie you really dont want them to get busy tone coz they might call a competitor)then use erlang C.
Bear in mind, ALL tables are based on various assumptions, most of which are marginal acuracy, so the results are at best an educated estimate.